1. Field of the Invention
The present invention relates to a keyswitch assembly and, more particularly, to a keyswitch assembly provided with a key restrained from horizontal movement and from free vertical movement, both when depressed and when not depressed. The key is suitable for use on a thin keyboard for portable word processors, personal computers and the like.
2. Description of the Related Art
Known keyswitch assemblies are disclosed in U.S. Pat. Nos. 4,580,022 ('022) and 4,902,862 ('862). These prior art keyswitch assemblies are provided with a large key, such as a space key or a return key, which has a construction capable of preventing the key from tilting when depressed.
The prior art keyswitch assembly proposed in the '022 patent has two pairs of key supports each formed by pivotally joining two support levers provided with pins at their opposite ends in a scissors-like form, a key supported on the key supports and provided with a pushing part, a switching member disposed apart from the center of the key, and a key guide for guiding the key for vertical movement. When the key is depressed, the pins of the support levers slide horizontally along pin guides formed on the back surface of the key and on the upper surface of a base plate, and the pushing part of the key slides vertically along the key guide to push the switching member.
The keyswitch assembly proposed in the '862 patent basically is the same in construction as the keyswitch assembly proposed in the '022 patent and is characterized by the scissors-like key supports designed to facilitate attaching the key thereto.
These prior art keyswitch assemblies are capable of maintaining the large key, such as the space key, in a horizontal position during the vertical movement of the key regardless of the point of application of pressure on the key when the key is depressed.
As is obvious from the drawings of the '022 and '862 patents, the pins formed at the opposite ends of the support levers of the scissors-like key supports are guided for horizontal movement by the pin guides formed on the back surface of the key and on the upper surface of the base plate. However, the keyswitch assemblies have no means for restraining the pins formed at the lower ends of the support levers from movement in a horizontal direction other than the horizontal direction along the pin guides formed on the upper surface of the base plate.
Accordingly, it is highly possible that the scissors-like key supports move needlessly in horizontal directions, both when the key is depressed and when the key is not depressed. When depressing the key, in particular, the needless horizontal movement of the scissors-like key supports spoils the touch of the key and, in the worst case, it is possible that the needless horizontal movement of the scissors-like key supports makes the key unable to operate the switching member.
Both the prior art keyswitch assemblies provide no means to prevent the needless vertical movement of the key when the key is not depressed. Therefore, the key is moved vertically by a light touch to the key, which also spoils the touch of the key.